Automatic control of a mold opening/closing speed through a program has been known in a mold opening controller using a hydraulic circuit in injection molding machines so as to improve an operation efficiency.
Such an apparatus generally controls a flow rate regulating valve disposed in a hydraulic circuit by the use of a limit switch and a timer, or has the flow rate regulating valve comprising a specific servo valve, as is known in the art. However, such an apparatus involves the problem of low controllability in the case of the former because response of the valve is poor, and the problem of a high production cost in the case of the latter because the servo valve is expensive.
Therefore, the applicant of this invention developed a mold opening controller which has high controllability and is relatively economical, and filed an application for a patent under the Japanese Patent Publication No. 3418/1988.
The apparatus comprises a flow rate regulating valve and a pressure regulating valve that are disposed in the hydraulic circuit, and a signal generator for controlling the opening of each of the flow rate regulating valve and the pressure regulating valve through a position sensor, so that the moving speed of a movable mold at an arbitrary position may be set arbitrarily. According to this apparatus, therefore, the moving speed of the movable mold or in other words, the mold opening speed, may be set to an optimum level by disposing a predetermined number of signal generators and setting appropriately the position of each signal generator relative to the movable mold and the signal quantity at this position.
However, the apparatus described hereinbefore has yet left the following critical problems still to be improved.
First of all, in a mold opening/closing apparatus for injection molding machines the acceleration/deceleration of a movable mold, particularly the acceleration/deceleration at the time of completion of mold closing and mold opening, must be set to those values which do not apply any shock to the mold opening/closing apparatus and which are as high as possible. However, these optimum acceleration/deceleration and optimum acceleration/deceleration positions vary with the kind of mold opening/closing apparatuses and with the kind of molds used even in the same mold opening/closing apparatus. In the mold opening controller described above, however, the optimum acceleration/deceleration positions and optimum acceleration/deceleration must be reset whenever the mold is changed. This change of setting is made by the repetition of a trial-and-error system and moreover, since a relatively large number of signal generators are disposed, this operation needs a great deal of labor and a high level of skill.
Further, the mold opening controller described above may be produced relatively economically but is relatively complicated in structure because a large number of signal generators are required.